The study of thermal, microstructural and magnetic propertiesof manganese–zinc ferrite prepared by co-precipitation method usingdifferent precipitants

Irena Szczygieł1 • Katarzyna Winiarska1 • Agnieszka Sobianowska-Turek2

Received: 30 October 2017 / Accepted: 25 May 2018 / Published online: 4 June 2018� The Author(s) 2018

AbstractMn–Zn ferrite was prepared from the solution after acid leaching of spent batteries by co-precipitation method using

ammonia oxalate, sodium carbonate and sodium hydroxide as precipitating agents. The co-precipitation process was

performed at temperature of over 50 �C by continuous magnetic stirring. The precipitates were pre-sintered at 850 �C in

air. Dilatometric study has revealed that lowest shrinkage (only 5.6%) showed a material obtained from an oxalate

precipitant. After pressing and high-temperature sintering at 1325 �C, it showed both insufficient density and the presence

of pores, which contribute to the deterioration in the magnetic properties of the ferrites: the low magnetic permeability

value and high magnetic losses. Ferrite prepared from hydroxide and carbonate precipitant showed a much higher

shrinkage, sintered density and much higher magnetic permeability compared with the ferrite prepared from oxalate

precursor.

Keywords Mn–Zn ferrite � Co-precipitation � Battery scrap � Microstructure � Magnetic properties � TGA–DTA/DIL/XRD/

SEM

Introduction

Mn–Zn ferrites are important group of soft magnetic

materials commonly used in microelectronics, e.g., in

transformer cores, choke coils and electromagnetic inter-

ference devices (EMI). High initial magnetic permeability,

electrical resistivity and low core losses at high frequencies

are the most important properties determining the scope of

their applicability. The magnetic properties of Mn–Zn

ferrites exploited in a particular application depend on their

structure (crystal structure and elemental composition) and

microstructure (density, porosity, the size and shape of

particles and pores) which are determined by the synthesis

conditions, such as the sintering time and temperature. On

the industrial scale, ferrites are produced by the ceramic

method. The bottom-up nanotechnology approach, includ-

ing soft chemical method, allows to synthesize homoge-

neous materials with defined morphology. Among these

methods, especially sol–gel autocombustion [1–6], co-

precipitation [7, 8], the hydrothermal and solvothermal

[9–11], the reverse micelles [12] and the mechanochemical

[13] methods have been extensively studied in the last

years. Ferrite produced by chemical methods is often

characterized by unique properties suitable for new

advanced application, i.e., magnetic high-density infor-

mation storage or drug delivery or contrast agent in bio-

medicine [14–18]. Ferrite powders obtained by low-

temperature synthesis due to their metastable character and

high activity can be used in catalysis [3, 19, 20]. Besides

the research on ferrite preparation by chemical methods,

there are reports of the possibility of Mn–Zn ferrites syn-

thesis from battery waste [21–29]. Battery scrap, especially

Electronic supplementary material The online version of thisarticle (https://doi.org/10.1007/s10973-018-7417-2) containssupplementary material, which is available to authorizedusers.

& Katarzyna Winiarska

katarzyna.winiarska@ue.wroc.pl

1 Department of Inorganic Chemistry, Faculty of Engineering

and Economics, Wrocław University of Economics,

Komandorska 118/120, 53-345 Wrocław, Poland

2 Division on Waste Technology and Land Remediation,

Faculty of Environmental Engineering, Wrocław University

of Science and Technology, Wybrze _ze Wyspianskiego 27,

Wrocław, Poland

123

Journal of Thermal Analysis and Calorimetry (2018) 134:51–57https://doi.org/10.1007/s10973-018-7417-2(0123456789().,-volV)(0123456789().,-volV)

Zn–C and Zn–Mn battery, due to its qualitative and

quantitative composition is the ideal by-product for

receiving Mn–Zn ferrite. Both in Poland and in Europe,

processing of waste batteries and accumulators is still an

important aspect of waste management. The Directive of

the European Parliament and of the Council of 26

September 2006 [30] defines the minimum levels of col-

lection and recycling of waste batteries and accumulators

and encourages to create new technologies of their pro-

cessing. Proposed in the literature methods of treating used

batteries rely on mechanical crushing and then leaching

with sulfuric [21, 22], hydrochloric [23] or nitric acid

[24, 25]. Ferrite can be prepared from such solutions by co-

precipitation [26–28] or by combustion methods in the

presence of citric acid (as a fuel) and nitrate ions, usually

derived from nitric acid leaching of crushed battery waste

(as an oxidant) [24, 25, 29]. The degree of leaching Mn, Zn

and Fe—main components of ferrite, and the microstruc-

ture and phase composition of the obtained product were

studied, but only Nan et al. [21] and Kim et al. [27]

characterized the magnetic properties of ferrites prepared

from waste battery. They found that saturation magneti-

zation of the powders obtained by co-precipitation is sim-

ilar to that of Mn–Zn ferrites synthesized by other chemical

methods.

The aim of this study is synthesis of Mn–Zn ferrites by

co-precipitation from the solution after acid leaching of

battery waste and determination of the effect of the applied

precipitating agents on the thermal, microstructural and

magnetic properties of the obtained powders. The solution

after leaching of battery mass by sulfuric acid is rich in Zn

and Mn ions and enriched in a stoichiometric amount of

FeSO4, a good source to prepare microcrystalline Mn–Zn

ferrites. The effect of the grain size of the ferrite powders

on shrinkage during sintering of compressed samples and

magnetic properties is discussed in the paper.

Experimental

Mn–Zn ferrite preparation

Mn–Zn ferrites were obtained from solution after battery

scrap leaching with the sulfuric acid (VI). A detailed

description of the leaching process containing the selection

of leaching parameters is given in [31, 32]. The degree of

leaching was * 85–95% for zinc and 25–30% for man-

ganese. Therefore, the solution was enriched with appro-

priate amount of manganese(II) and iron(II) sulfates in

order to get the Mn0.6Zn0.4Fe2O4 stoichiometry. Co-pre-

cipitation was performed under previously predetermined

conditions for three precipitants: ammonium oxalate

(T = 60 �C, t = 1.5 h, pH = 4, sample denoted as ‘‘S1’’),

sodium carbonate (T = 50 �C, t = 3 h, pH = 8.5, sample

denoted as ‘‘S2’’) and sodium hydroxide (T = 60 �C,

t = 3 h, pH = 10, sample denoted as ‘‘S3’’). A precipitating

agent was added sequentially to the solution and, if

required, the pH of the mixture was adjusted with the use

of ammonia 25 vol%. The obtained suspension was heated

under continuous magnetic stirring. The precipitates were

then filtered under reduced pressure and thoroughly washed

with distilled water to remove the remaining sulfates. The

received sludge was dried in a drying chamber at 105 �Cfor 24 h, and then, it was subjected to a typical procedure

like ceramic ferrites: pre-sintering at 850 �C, grinding,

pressing and at last sintering during the final microstruc-

tural and magnetic properties are achieved. The finishing

sintering process was carried out at 1325 �C for 3 h in an

oxygen atmosphere. Oxygen partial pressure was con-

trolled according to procedure given by Schaller [33] and

Morineau et al. [34].

Mn–Zn ferrite characterization

Identification and phase composition of prepared ferrite

powders were determined by X-ray diffraction analysis at

room temperature on Siemens D-500 Diffractometer (with

radiation CuKa and wavelength 1.54051 A). The X-ray

diffraction data were obtained at the angles 5–80� with a

step of 0.04� and time 1 s per step. The phases were

identified by utilizing the ICDD PDF-4 database. Scanning

electron microscopy (FEI QuantaTM250) allowed to

determine a morphology and grains’ size. All the samples

for scanning electron microscopic observation were pre-

viously sputtered with a thin (* 10 nm) layer of carbon.

Thermoanalytical analysis (DTA/DTG/TGA) was carried

out with a derivatograph type 3427 (MOM, Hungary), from

20 �C up to 1350 �C under air (heating rate: 7.5 �C min-1,

reference material: a-alumina, platinum crucibles, Pt/

PtRh10 thermocouple). Dimensional changes of ferrite

powders were provided by dilatometry (DIL) on the DIL

402 dilatometer (Netzsch) in the temperature range of

25–1300 �C with a step of 2� min-1. The powders were

compressed into pellets (with addition 10 vol% of WAX

binder) and heated up to 1300 �C. For magnetic testing,

ferrite powders after pre-sintering at 850 �C were pressed

into toroidal rings. The density of the finally sintered tor-

oidal specimens was measured by Archimedes water den-

sity method. The magnetic properties were performed on

an EMMA device. The power losses were measured at

25 kHz under magnetic field of 200 mT. Loss factor was

investigated in 25 �C, 0.1 mT and frequency range of

25–1000 Hz. Permeability was tested in a frequency range

of 25–1000 Hz and field 0.1 mT in two independent

measurements at constant temperature of 25 �C or variable

temperature in the 25–85 �C range.

52 I. Szczygieł et al.

123

Results

DTA–TGA analysis performed on precipitates obtained

from ammonia oxalate, sodium carbonate and sodium

hydroxide enabled to determine the conditions of pre-sin-

tering and final sintering of powders. In the DTA–TGA

heating curves for the oxalate precipitate, two thermal

effects at onset temperatures of * 200 �C and maximum

at 280 �C appeared (Fig. 1a). The first endothermic effect

is associated with the dehydration of the precipitated

powder. The next, exothermic effect at 280 �C is associ-

ated with the decomposition of precipitate and formation of

oxides. The exothermal reaction is accompanied by a sig-

nificant mass loss of approximately 55%. Above 400 �C,

TGA curve did not show any mass change. A slight

exothermic effect on the DTA curve at about 1300 �Cindicates that the spinel phase is ultimately formed at this

temperature. The carbonate deposit (Fig. 1b) undergoes

dehydration at about 100 �C and a significant mass loss

(about 25%) observed at TGA curve begins and finally

ends at 850 �C. At 280 �C, there is a pronounced

endothermic effect on the DTA curve associated with the

decomposition of carbonates into the oxides. Also, a small

exothermic effect was observed for this sample at about

1300 �C. For the hydroxide precipitate (Fig. 1c), small

changes are visible on the DTA curve. They are connected

with a slight mass loss of approximately 7% in 200–400 �Crange (TGA). Dehydration, which was associated with the

partial oxidation of Mn, Zn and Fe, occurs in this tem-

perature range. There is no mass change above 400 �C at

TGA curve. Similar to the previously described oxalate and

carbonate precipitates, a small exothermic effect was

observed at * 1300 �C. Based on the conducted DTA/

TGA research, there was established final sintering tem-

perature of the precipitates as 1325 �C.

The relative contribution of each oxide in Mn–Zn ferrite

obtained from solution after battery waste leaching and

finally sintered at 1325 �C was investigated by X-ray flu-

orescence spectroscopy method (XRF). On the basis of

analysis data (Table 1), it can be concluded that relative

contribution of main ferrite oxides: Fe2O3, MnO and ZnO,

is close to the expected composition (Mn0.6Zn0.4Fe2O4).

The iron oxide contribution in sample prepared from

hydroxide precipitate (S3) was slightly lower than in others

samples. The Zn–C and Zn–Mn waste battery stream

besides Zn, Mn and Fe usually contains other elements

[35]. Therefore, the amount of other metal oxides from

battery scrap in prepared materials was determined and is

listed in Table 1. The MgO content in the S1 and S3

samples exceeded 3%, whereas in S2 sample it amounted

to nearly 1%. SiO2, TiO2 and CaO amounts were not higher

than 0.5%. It should be noted that the contribution of other

impurities (Co, Cu, Ni oxides) was small; however, their

presence may contribute to deterioration in structural and

magnetic properties in Mn–Zn ferrite. Considering the

higher than expected magnesia (MgO) content (see

Table 1), the composition of the obtained materials can be

described as formulas: Mn0.52Zn0.38Mg0.10Fe2O4 (for

samples S1 and S3) and Mn0.56Zn0.41Mg0.03Fe2O4 (for S2

sample).

The ferrite powders after pre-sintering at 850 �C are

almost two phases. The X-ray diffraction analysis (Sup-

plementary material 1) revealed that apart from spinel

phase, an a-hematite is crystallized. The relative mass

fraction of the non-magnetic phase in the pre-sin-

tered ferrites was determined on the basis of the ratio of the

100

175

Δm/m

g

1501251007550250

125

50Δm/m

g

250

DTG

DTA

T EX

O

1007550250

DTG

DTA

T

TGA

EX

O

Δm/m

g

DTG

DTA

TT

TGA

EX

O

300 500 700 900 1100 1300

T/°C T/°C

100 300 500 700 900 1100 1300 100 300 500 700 900 1100 1300

(a) (b) (c)

T/°C

Fig. 1 The DTA/DTG/TGA curves of precipitates prepared using a ammonia oxalate, b sodium carbonate, c sodium hydroxide as precipitating

agent

The study of thermal, microstructural and magnetic properties 53

123

major hematite-derived peaks intensity to the intensity of

peak characteristic for the spinel phase. Ferrite powder

prepared from oxalate precipitate (S1) was characterized by

the smallest part of hematite amounted at about 10%,

whereas the ferrite prepared from carbonate precursor (S2)

included 25% of hematite. Slightly lower (20%) hematite

part was in S3 sample, which was synthesized by the use of

sodium hydroxide as precipitating agent. The XRD patterns

of ferrite samples sintered at 1325 �C in controlled oxygen

atmosphere are shown in Fig. 2. The diffraction peaks are

slightly shifted toward lower 2H angles compared with

diffraction peaks’ position for spinel cubic structure of

Mn–Zn ferrite (JCPDS-ICDD Card No. 01-074-2401). In

addition, the peaks at higher angles have greater shift (but

not the same 2H value) compared with those at smaller 2Hvalues. According to the Bragg’s law, it suggests an

expansion of the spinel unit cell. An increase in cubic

spinel lattice can be caused by the incorporation of other

cations (as impurities) from the solution after leaching into

the spinel lattice. The XRD reflections originating in these

secondary phases are not visible in the XRD patterns,

because their content is beyond the detection level for the

powder XRD method, despite the fact that the XRF shows

a presence of other metal oxides.

A linear shrinkage for initially sintered at 850 �C and

then pressed ferrite powders prepared by co-precipitation

was investigated by dilatometry, DIL (Fig. 3). The density

of ferrites determined before the dilatometric measurement

was successively amounted to 2770, 2730 and

2690 kg m-3 for S1, S2 and S3, respectively. The smallest

shrinkage, and in consequence density, was observed for

the material obtained from the oxalate precipitate (S1). The

shrinkage was only 5.6% and the densification process

started at much higher temperature (1050 �C) than for the

other samples. This high temperature, in which the material

undergoes shrinkage, is not favorable due to lower final

density. For comparison, the ferrites obtained from the

carbonate (S2) and hydroxide precipitate (S3), whose

densification processes started at 830 and 700 �C, had a

significantly higher shrinkage (21.8 and 21.7%). The den-

sity of samples (after final sintered toroid) was determined

based on the Archimedes’ principle. The density of S1

sample amounted to 4189 kg m-3 and differed signifi-

cantly from the density of Mn–Zn ferrite (4900 kg m-3)

commercially produced [36]. The shrinkage for S2 and S3

is similar to ferrite produced commercially by ceramic

method (shrinkage amounted at about 20%), and these

samples were characterized by higher final density: 4412

and 4355 kg m-3 for S2 and S3, respectively. A slightly

lower density (4355 kg m-3) of material prepared from

carbonate precipitate (S2) may be due to higher densifica-

tion temperature.

For better characterization of the microstructure and

magnetic properties of the ferrites obtained from the spent

battery leach solution, they were compared with reference

Table 1 Relative contribution of metal oxides in prepared ferrites

Sample %Fe2O3 %MnO %ZnO %TiO2 %CaO %SiO2 %CoO %CuO %NiO %MgO %Al2O3

S1 67.76 18.76 13.45 0.034 0.177 0.202 0.020 0.020 0.064 3.640 0.017

S2 67.11 18.76 13.78 0.325 0.189 0.258 0.017 0.046 0.067 0.970 0.067

S3 66.82 18.90 13.95 0.334 0.055 0.274 0.018 0.044 0.067 3.520 0.069

15

Inte

nsity

/a.u

.

Spinel (JCPDS-ICDD Cart No. 01-074-2401)

2 /°20 25 30 35 40 45 50 55 60

θ

S1

S2

S3

Fig. 2 The XRD diffraction patterns of Mn–Zn ferrites sintered at

1325 �C

–20

–16

–12

–8

S1S2S3

dL/L

0/%

Temperature/°C

–4

0

0 300 600 900 1200 1500

Fig. 3 The temperature dependence of linear shrinkage on com-

pressed ferrite material

54 I. Szczygieł et al.

123

samples received from Ferroxcube. As it is shown in

Fig. 4, the morphology of ferrites prepared after pressing

and sintering at high temperature is diverse. The ferrite

obtained from oxalate precursor (S1) is characterized by

fine and homogeneous microstructure. The grain is roughly

spherical, with size less than 5 lm (Fig. 4a). It can be seen

in the magnification inter grains are free spaces and pores.

The pronounced porosity results from insufficient densifi-

cation are reflected in low density. On the other hand, Mn–

Zn ferrite prepared from carbonate (S2) and hydroxide (S3)

precursors is characterized by non-uniform microstructure,

which consists of grains different in size (Fig. 4b, c). An

abnormal, exaggerated grain growth effect favors inter-

granular pore formation. The promoter of the duplex

structures formation can be the presence of SiO2 in larger

quantities [37]. By contrast, the reference sample from

Ferroxcube obtained by conventional ceramic method

(Fig. 4d) possesses comparatively homogeneous

microstructure. Pores or gaps are not visible, which means

that material is compacted properly. However, grains are

30 μm 30 μm

(a) (c)

(b) (d)

Fig. 4 SEM microphotographs of prepared Mn–Zn ferrite a S1, b S2,

c S3, d HighPerm grade from Ferroxcube

Table 2 Magnetic properties of ferrites prepared by co-precipitation and conventional ceramic method (reference samples)

Measurement conditions Temperature/�C Sample FXC reference sample

S1 S2 S3 Power gradea HighPerm gradea

Initial permeability

10 kHz; 0.1 mT 10 226 2649 2605 5694 11,352

30 kHz; 0.1 mT 25 237 2799 2887 6330 12,500

100 kHz; 0.1 mT 40 248 2963 3226 7255 13,452

200 kHz; 0.1 mT 55 259 3080 3626 8361 14,134

400 kHz; 0.1 mT 70 268 3151 4120 9623 14,734

1000 kHz; 0.1 mT 85 275 3150 4696 10,853 15,403

Loss factor

100 kHz; 0.1 mT 25 – – – – 0.9

200 kHz; 0.1 mT 25 – – – – 8.4

400 kHz; 0.1 mT 25 – 23 23 1 29

1000 kHz; 0.1 mT 25 110 118 62 26 164

Power loss/mW cm-3

25 kHz; 200 mT 25 2390.7 Not able to measure Not able to measure 31.8 14.1

90 5143.6 5.9 26.8

95 5559.6 4.3 28.8

100 6350.7 4.1 30.8

105 6727.9 4.7 33.8

110 7394.2 5.3 38.6

aCommercially available ring core—Ferroxcube

16.0 k

14.0 k

12.0 k

10.0 k

8.0 k

6.0 k

4.0 k

2.0 k

0.00 200 400 600 800 1000

S1S2S3Power gradeHigh perm grade

Frequency/kHz

Initi

al p

erm

eabi

lity

Fig. 5 Relative initial permeability as a function of frequency

(0.1 mT, 25 �C)

The study of thermal, microstructural and magnetic properties 55

123

relatively large in the range of 5–20 lm. Such differences

between the microstructure of materials obtained from

battery waste and those synthesized by the traditional

ceramic method explain the deterioration of the magnetic

properties of the former ferrites (see Table 2, Fig. 5).

Magnetic properties were investigated on EMMA

device. An initial permeability (li), loss factor (tg d/li) and

power loss (Pv) were measured and are summarized in

Table 2. The samples S2 and S3 display high values of

initial permeability; however, these values are almost twice

lower than reference sample ‘‘Power grade’’ (from Fer-

roxcube). The initial permeability for sample S1 was def-

initely lower, but independent of frequency and

temperature. Figure 5 shows relationships between initial

permeability and frequency at 25 �C, and in this case,

sample S1 is characterized also by lowest permeability.

Samples S2 and S3 exhibit comparable values of initial

permeability, slightly changing with frequency. It is inter-

esting to note that the obtained values of initial perme-

ability correspond quite well to results described in the

literature for ferrites synthesized by co-precipitation

method [38]. Mangalaraja et al. [6] suggested that the low

initial permeability value for materials prepared by chem-

ical method can be associated with higher value of aniso-

tropy constant and microstructure of prepared ferrite

(grains size, grain and pore distribution). Low value of

initial permeability for samples prepared from waste bat-

tery scrap can be a result of the presence of intergranular

pores, which in the magnetic field holds the domain walls

back to the rotation.

Power loss was measured at frequency of 25 kHz and

magnetic field 200 mT. The S2 and S3 samples are char-

acterized by high power loss and the measurements were

unfeasible. Power loss for sample S1 was measured;

however, it was still higher than that for reference samples.

The studied materials were characterized by loss factor

(tg d/li) at higher frequency comparable to samples from

Ferroxcube. The loss factor value in Mn–Zn ferrites

depends on composition (relation between Fe2O3, MnO

and ZnO) and microstructure. Kogias et al. [39] explained

that lower sintered density reduces the magnetic flux per

unit volume, reduces li and increases Pv. In order to pre-

pare ferrite characterized by low losses at high frequencies,

it is necessary to choose both composition and additives

which will minimize constant anisotropy and will produce

a material with uniform grain size, without defects, pores

or impurities [40].

Conclusions

Mn–Zn ferrites obtained by co-precipitation from the acid

solution after leaching of the waste batteries differ in

microstructure and magnetic properties according to the

precipitant used. DTA–TGA study indicates thermal

decomposition of precipitants at low temperature

(200–400 �C) with mass change. For all samples, slightly

exothermic effect connected with an a-hematite phase

transformation to spinel at DTA curve is visible. The phase

transformation was also confirmed in XRD studies. The a-

hematite is present in powders after pre-sintering step,

whereas after final pressing and high-temperature sintering

at 1325 �C only ferrite phase appears at XRD spectra.

Ferrite powders prepared after co-precipitation have been

subjected to typical processing (grinding-pressing-sinter-

ing) as commercial produced materials. Ferrites prepared

from carbonate and hydroxide precipitant show shrinkage

similar to ferrite produced on an industrial scale (about

20%). However, an exaggerated grain growth effect and

intergranular pores in pressed ferrites (S2 and S3) caused

lower initial permeability, which changes with frequency in

the same way for these samples. Ferrite toroid prepared

from oxalate precursor possesses lower shrinkage (only

5.6%), lower density but uniform and fine microstructure.

The initial permeability for this sample was definitely

lower, but independent of frequency and temperature. The

results of magnetic testing compared to commercial ferrites

are not fully satisfactory. However, optimization of the

pressing and sintering processes of such fine powders could

in future contribute to better compaction. The selection of

additives to reduce excessive grain growth in samples

obtained from the hydroxide and carbonate precursors

would contribute to more uniform microstructure. The

reduction in these samples of power losses with a similar

permeability value would allow to use them in power

switching application. A slight shrinkage of the sample

obtained from the oxalate precursor for application reasons

appears to be interesting as it allows the possibility of

designing a material with a large tolerance of shape.

Acknowledgements The authors would like to thank Magdalena

Pawlak and Dietmar Holtz from Ferroxcube for the magnetic mea-

surements and the assistance provided.

Open Access This article is distributed under the terms of the Creative

Commons Attribution 4.0 International License (http://creative

commons.org/licenses/by/4.0/), which permits unrestricted use, dis-

tribution, and reproduction in any medium, provided you give

appropriate credit to the original author(s) and the source, provide a

link to the Creative Commons license, and indicate if changes were

made.

56 I. Szczygieł et al.

123

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